This invention relates to an absorption machine and, more particularly, to an improved absorption heat pump/refrigeration machine utilizing a desorber loop and a resorber loop to increase efficiency.
In a typical single effect system, water is generally the refrigerant and lithium bromide is generally the absorbent, and together they are called a solution pair. Some systems employ high temperature solution pairs that are capable of operating at higher generator temperatures to increase efficiency but are precluded from operating at lower evaporator temperatures due to the possibility of freezing and crystallization of the refrigerant, while other chemical systems capable of operating at lower evaporator temperatures, even temperatures below the freezing point of water, could not operate at the higher generator temperatures, which are a consequence of the lower evaporator temperature, without stability problems. Consequently, a single effect system is generally limited in the selection of higher and lower operating temperatures in the generator and evaporator.
Absorption cycles of a single effect type generally comprise a generator for heating a weak or relatively dilute absorbent solution to generate vapor of refrigerant, a condenser for condensing the vapor of refrigerant, an evaporator for evaporating the condensed refrigerant to provide cooling, and an absorber for absorbing the refrigerant vapor from the evaporator into a strong or relatively concentrated absorbent solution. However, the thermal efficiency (coefficient of performance of COP) of a single effect type absorption system is relatively low and ordinarily about 0.6-0.8. Accordingly, with a view toward increasing the thermal efficiency of absorption cycles, two stage generator type absorption units have been developed in which a further generator is additionally provided in the single effect type absorption refrigerator such that the high temperature vapor of refrigerant generated in a first generator is utilized to heat a second generator. In general, a two stage generator type absorption unit comprises a high temperature generator, a low temperature generator, a condenser, an evaporator, an absorber, a high temperature heat exchanger and a low temperature heat exchanger. In the high temperature generator, a refrigerant dissolved in a solution, such as an aqueous solution of lithium bromide, is heated by heating means to discharge the dissolved refrigerant as vapor. Further, in one configuration, the discharged refrigerant vapor is fed through a bundle of heat transfer tubes to the low temperature generator to heat the weak solution supplied from the absorber, and while the refrigerant in the weak solution is discharged therefrom as vapor the vapor from the strong solution is cooled by the latent heat of evaporation nearly all is and condensed prior to entering the condenser. The refrigerant vapor produced in the low temperature generator is supplied to the condenser and cooled by cooling means thereof and then condensed. This condensed refrigerant is generally sprayed into the evaporator, thereby cooling the fluid means which cools a load. Moreover, the solution concentrated by discharging the refrigerant vapor in the high temperature generator is fed to the high temperature heat exchanger in heat exchange relationship with the low temperature weak solution supplied from the low temperature generator, thereby suitably lowering its temperature, and then fed to the low temperature heat exchanger in heat exchange relationship with the weak solution derived from the absorber. Then the solution flows to the absorber which is cooled by cooling means. Thus, solution sprayed into the absorber absorbs the refrigerant vapor supplied from the evaporator, and provides a weak solution. This solution is further directed to the low temperature heat exchanger as described above.
In this manner, the two stage generator type absorption is arranged such that the external heat supplied is utilized twice, once in the high and once in the low temperature generator, thus the thermal efficiency typically increases up to 50/60% in comparison with the single effect type system.